This invention relates generally to gas turbine engines and, more particularly, to fuel delivery systems which include thermally compatible fuel nozzles for gas turbine engines.
Maximizing the life cycle of fuel nozzles installed within gas turbine engines extends the longevity of the gas turbine engine. Fuel nozzles are subjected to high temperatures when the gas turbine engine is operating. Such high temperatures induce thermal stresses on the fuel nozzles which often lead to a failure of the fuel nozzles or ultimately, a failure of the gas turbine engine.
Known fuel delivery systems include a plurality of fuel nozzles which include a delivery system and a support system. Each delivery system delivers fuel to the gas turbine engine and is supported and shielded within the gas turbine engine with the support system. The support system surrounds the delivery system and is thus subjected to higher temperatures than the supply system. To minimize the effects of the high temperatures, the support system is typically fabricated from a first material which has material characteristics, including a coefficient of expansion, which permit the support system to withstand the potentially high temperatures.
The delivery system is disposed within the support system and fluid flowing within the delivery system cools the delivery system. Accordingly, the delivery system is subjected to much lower temperatures. Typically the delivery system is fabricated from either the same material or a second material which is resilient to a lower range of temperatures and has a coefficient of expansion that is approximately equal to the support system material coefficient of expansion. As a result of the operating temperature differential between the delivery system and the support system, thermal stresses develop between the delivery system and support system as each system thermally expands.
In an exemplary embodiment, a fuel injection system for use with a gas turbine engine includes a plurality of thermally compatible fuel nozzles. Each fuel nozzle includes a delivery system to deliver a fluid supply to the gas turbine engine and a support system for supporting the delivery system. Each delivery system is fabricated from a first material which has a first coefficient of expansion and is disposed within a respective support system. Each support system shields a respective delivery system and is fabricated from a second material which has a second coefficient of expansion. The second coefficient of expansion is approximately half the coefficient of expansion of the first material. A slip joint is disposed between the support system and the delivery system and compensates between the support system and the delivery system coefficients of expansion, such that both systems thermally expand in proportion to each respective system""s material coefficient of expansion.
During operation, the delivery system is subjected to lower temperatures than the support system. Because the support system is fabricated from a material having a low coefficient of expansion and the delivery system is fabricated from a material having a high coefficient of expansion, differential expansion is less than if the two systems were fabricated from the same material. As a result, the effects of thermal expansion are minimized between the delivery system and the support system as each system thermally expands.